This invention relates generally to gas turbine components, and more particularly to cooled turbine airfoils.
Cooling circuits inside modern high pressure turbine blades typically have two parallel cooling circuits adjacent to each other. A leading edge circuit is a single-pass radially outward flow passage with leading edge film cooling holes and a tip opening. A mid-chord and trailing edge circuit is a multiple-pass serpentine with film cooling holes exiting to the pressure side of the blade. The leading edge circuit and mid-chord circuit are commonly fed a coolant from the airfoil dovetail and split into two separated passages at the blade root. Being a single pass structure, the leading edge circuit can not efficiently utilize the full capacity of the coolant, which is typically compressor discharge air. The Coolant in the leading edge channel exits through the leading edge film holes and the tip hole. To provide sufficient escape area for the particles entrained in the coolant supply system, the tip openings take the form of relatively large “dust holes” for each cooling circuit. These dust holes typically are larger than the film cooling holes. Air exiting from the dust holes can not provide cooling to the blade as efficiently as the relatively smaller film cooling holes.
Accordingly, there is a need for an efficiently cooled airfoil having a small number of dust holes.